Mount Adams is a huge stratovolcano in southern Washington and the state’s second-highest mountain, distinguished by its broad eighteen-mile base and dominant place in the Cascade Volcanic Arc. Formed over hundreds of thousands of years, its present cone developed between about forty thousand and ten thousand years ago, and it is still considered active, with potential hazards including lahars, pyroclastic flows, and ashfall. The mountain features a wide summit plateau, twelve named glaciers, and sharply contrasting ecosystems on its wetter west and drier east sides. Long important in Indigenous traditions, it later received its English name through a mapping error and remains a comparatively remote center for recreation.